Abstract: Measured the reaction times (RTs) of 25 schizophrenic (SCZ), 69 matched normal, and 14 bipolar Ss to a tone preceded by a preparatory interval (PI) of varying length. RTs increase when the PI for the immediately preceding trial (PPI) is longer than the PI for the current trial. Several studies have shown that this PPI effect is heightened in schizophrenia. The authors replicated this finding. However, they found that the size of the PPI effect within groups increased with overall slowness and that the least squares regression line relating the PPI effect difference score to overall slowness did not differ between groups, nor did SCZ Ss' regression line differ from that of normal Ss. Group differences on the PPI effect were also analyzed by taking residuals for members of all groups from the normal Ss' regression line of the PPI effect difference score on overall slowness. Groups did not differ on these residuals, nor did SCZ Ss differ from normal Ss. The authors conclude that the heightening of the PPI effect in schizophrenia is like that observed in equally slow normal Ss. This finding suggests that the PPI effect does not appear to be a promising marker of a distinctive SCZ pathology. (PsycINFO Database Record (c) 2012 APA, all rights reserved)